This invention relates generally to turbines, and more particularly to convective cooling of mating areas of side walls between the seal slots and hot gas paths of turbine nozzle segments.
In at least some known industrial turbines, one or more of the nozzle stages are cooled by passing a cooling medium through a plenum in each nozzle segment portion forming part of the outer band and through one or more nozzle vanes to cool the nozzles, and into a plenum in a corresponding inner band portion. In some nozzle segments, the cooling medium then flows through the inner band portion and again through the one or more nozzle vanes prior to being discharged. In other nozzle segments, the cooling medium flows only once through each nozzle segment. Each of the nozzle segments includes inner and outer band portions and one or more nozzle vanes, and are typically cast.
The mating surfaces of the band portions include seal slots to accommodate seals that extend between adjacent band portions. Impingement air used to cool part of the band portions does not reach the area between the seal slots and the hot gases because of the seal slots. High metal temperatures can then develop in this area which can cause metal erosion and crack development due to high thermal stresses. In some known turbine nozzles, cooling holes feed cooling air from the turbine vane cavity to the mating faces. However, such an arrangement requires a significant increase of cooling flow and reduces turbine efficiency and results in increased heat rate.